The present invention relates to embodiments of a method, system and controller for determining whether to brake a trailer in the absence of an air signal on a pneumatic control line. A trailer that is part of an air braked tractor-trailer combination generally receives a service brake demand signal via the pneumatic control line between the tractor and trailer. However, a typical trailer controller cannot determine if there is a problem in the pneumatic control line that may prevent the driver actuated brake demand from reaching the trailer. One problem that may cause this issue is if the driver has forgotten to connect the gladhands, which are pneumatic connectors used to join the tractor pneumatic control line to the trailer pneumatic control line. Another problem may be a loss of the connection of the gladhands between the tractor and trailer during operation of the vehicle or an obstruction in the tractor or trailer pneumatic control lines. Another problem may be a broken or leaking pneumatic control line. If the driver applies the service brakes in the tractor and the trailer service brakes do not apply due to one of the aforementioned issues, the vehicle may not decelerate at the rate expected by the driver and the stability of the vehicle combination may be affected.
A brake-by-wire system, also known as electronic braking, transmits an electronic control signal indicative of the driver's brake demand from the tractor directly to the trailer and may be in addition to the air signal on the pneumatic control line. In one embodiment, the tractor and trailer communicate information, such as brake demand, between themselves over a serial communications bus, such as SAE J1939. However, typical tractor-trailer combination vehicles in the United States are not equipped with a brake-by-wire system. In addition, the tractor and trailer do not share a serial communications bus connection, even if the trailer is equipped with an anti-lock brake or stability system controller. Therefore, these trailers do not have a redundant method of receiving a brake demand signal if there is a problem with the air signal on the pneumatic control line. If there is no air signal received on the pneumatic control line, the trailer service brakes will not be applied. Therefore, there is a need for a system to determine whether to brake the trailer in a situation when there is a driver brake demand from the tractor, but the trailer does not receive the brake demand pneumatically.